Back to EveryPatent.com
United States Patent |
5,628,311
|
Mauze
|
May 13, 1997
|
Chemical sensor with variable volume sensor cell and method
Abstract
A chemical sensor having a sheath, an optical fiber bundle, a mirror, and a
mechanism associated with the optical fiber bundle for detecting light
interaction, wherein the optical fiber means or the mirror is slidably
disposed in the sheath, is provided. At least a portion of the sheath is
permeable to a fluid suspected of containing a target chemical. The
optical fiber bundle has a portion disposed in the sheath for emitting
light to cause optical interaction with the target chemical surrounded by
the sheath. The mirror is disposed in the sheath to reflect light emitted
by the optical fiber bundle.
Inventors:
|
Mauze; Ganapati R. (Sunnyvale, CA)
|
Assignee:
|
Hewlett-Packard Company (Palo Alto, CA)
|
Appl. No.:
|
520428 |
Filed:
|
August 29, 1995 |
Current U.S. Class: |
600/342; 422/82.06; 422/82.07; 600/314; 600/476 |
Intern'l Class: |
A61B 005/00 |
Field of Search: |
128/634,633-35,664-65
422/82-82.11
|
References Cited
U.S. Patent Documents
4785814 | Nov., 1988 | Kane et al.
| |
5096671 | Mar., 1992 | Kane et al. | 128/634.
|
5154890 | Oct., 1992 | Mauze et al.
| |
5176882 | Jan., 1993 | Gray et al.
| |
5305744 | Apr., 1994 | Pfeiffer et al. | 128/634.
|
5393493 | Feb., 1995 | Makino et al.
| |
5423320 | Jun., 1995 | Salzman et al. | 128/634.
|
5434084 | Jul., 1995 | Burgess, Jr. | 128/634.
|
Other References
Robert Kok and Pat Hogan, "The Development of an In Situ Fermentation
Electrode Calibrator", Biosensors 3 (1987/88) pp. 89-100.
|
Primary Examiner: Sykes; Angela D.
Assistant Examiner: Carter; Ryan
Claims
What is claimed is:
1. A chemical sensor, comprising:
(a) a sheath, having at least a portion permeable to a fluid suspected of
containing a target chemical, for surrounding a sample of said fluid;
(b) an optical fiber means having a portion disposed in the sheath for
emitting light to cause light interaction with the target chemical in the
sample of said fluid surrounded by the sheath;
(c) a mirror disposed in the sheath for reflecting light emitted by the
optical fiber means; and
(d) means associated with the optical fiber means for detecting the light
interaction;
wherein the sheath, optical fiber means, and mirror define a chamber for
including the fluid and wherein at least one of the optical fiber means
and the mirror is slidably disposed in the sheath to force the fluid
through the sheath.
2. The chemical sensor according to claim 1 wherein the optical fiber means
is slidably disposed in the sheath.
3. The chemical sensor according to claim 1 wherein the sheath is a
membrane permeable to the fluid but impervious to particulate matters.
4. The chemical sensor according to claim 2 wherein the membrane is
permeable to molecules smaller than 100,000 Daltons molecular weight.
5. The chemical sensor according to claim 1 wherein the sheath is
impervious to particulate matters of larger than 2.0 .mu.m.
6. The chemical sensor according to claim 1 wherein the sheath is
impervious to particulate matters of larger than 0.2 .mu.m.
7. The chemical sensor according to claim 1 wherein the optical fiber means
has at least 2 optical fibers each having a different sensing matrix
disposed thereon for sensing the light interaction.
8. The chemical sensor according to claim 1 wherein the optical fiber means
has at least 2 optical fibers each disposed at a different distance from
the mirror.
9. The chemical sensor according to claim 1 further comprising a porous
support surrounding the sheath for supporting the sheath as fluid is
forced therethrough from a location surrounded by the sheath.
10. The chemical sensor according to claim 1 wherein at least one of the
optical fiber means and the mirror is slidably disposed in the sheath to
increase the pressure in the chamber to force the fluid through the sheath
to dislodge particulate matters on the sheath outside the chamber.
11. The chemical sensor according to claim 1 wherein at least one of the
optical fiber means and the mirror is slidably disposed in the sheath to
decrease the pressure in the chamber to force the fluid through the sheath
into the chamber while keeping out particulate matters.
12. A chemical sensor, comprising:
(a) a sheath, having at least a portion permeable to a fluid suspected of
containing a target chemical, for surrounding a sample of said fluid, the
sheath being a membrane permeable to the fluid but impervious to
particulate matters;
(b) an optical fiber means having a portion disposed in the sheath for
emitting light to cause light interaction with the target chemical in the
sample of said fluid surrounded by the sheath;
(c) a minor disposed in the sheath for reflecting light emitted by the
optical fiber means; and
(d) means associated with the optical fiber means for detecting the light
interaction;
wherein the sheath, optical fiber means, and mirror define a chamber for
including the fluid and wherein at least one of the optical fiber means
and the mirror is slidably disposed in the sheath to vary the volume and
pressure in the chamber such that the fluid is forced through the sheath
into the chamber while keeping out the particulate matters when the volume
of the chamber is increased and to dislodge particulate matters on the
sheath outside the chamber when the volume of the chamber is reduced.
Description
FIELD OF THE INVENTION
The present invention relates to chemical sensors and methods for analyzing
target chemicals in a liquid. More particularly, the present invention
relates to chemical sensors that can be used in a liquid containing
particulate matters and methods of using and making such chemical sensors.
BACKGROUND
Chemical analyses are often important in evaluating the characteristics and
contents of a liquid. For example, in caring for a critically ill patient,
it is desirable to know the concentrations of, for example, gases (oxygen,
carbon dioxide, etc.) and ions (potassium, calcium, etc.) in the patient's
blood. Another example is the culturing of cells, such as in fermentation
(e.g., for the production of bacterial antibiotics). In such instances,
the levels of nutrients and gases in the liquid are monitored to provide a
suitable environment for cell growth and the production of desired
products.
Chemical sensors have been used in measuring chemical parameters in
liquids. For example, U.S. Pat. No. 4,785,814 (Kane) discloses an optical
probe for measuring pH and oxygen content in blood in a blood vessel
within a living body. The optical probe has an elongated flexible optical
fiber, the distal end of which is adapted to be inserted into a blood
vessel. A membrane constructed of a hydrophilic porous material containing
a pH sensitive dye is secured to the distal end of the optical fiber. This
membrane receives light from the optical fiber and returns light
therethrough to the proximal end of the fiber. Another example of using an
optical fiber in a chemical sensor is disclosed in U.S. Pat. No. 5,176,882
(Gray et. al.). The chemical sensor described by Gray et. al. is capable
of sensing more than one analyte. This sensor has two fiber optic sensor
cells, one of which is for measuring a combination of ionic species. A
second fiber optic sensor cell is used for measuring gaseous species. Each
of the sensor cells has a membrane that is permeable to the corresponding
ions and gases of interest.
Although the above chemical sensors are described as being suitable for use
with physiological samples, they will not function properly in highly
dispersive media (i.e., liquids containing particulate matters) such as
fermentation broths, sewage treatment streams, contents of fluidised bed
reactors, and slurries. A fermentation electrode calibrator has been
described by Kok and Hogan (Biosensors 3, 89-100, (1987/88)). This
calibrator (with an oxygen probe) is described as being suitable for use
in situ in a fermentor. Scrubbing tubes directed at a face of the oxygen
probe provide high velocity jets (of air or steam) for cleaning. However,
the calibrator of Kok and Hogan is mechanically complex and bulky, making
it unsuitable for use in a small liquid sample. What is needed is a
chemical sensor of relatively simple mechanical construction for
application in a liquid with particulate matters.
SUMMARY
The present invention provides a chemical sensor that can be used to
analyze analytes (i.e., target chemicals) dissolved in a sample liquid
(i.e., the volume of liquid to be analyzed) that has a liquid (i.e.,
solvent) and particulate matters (for example, fermentation broths, pond
water for environmental analysis, etc.). The chemical sensor has a sheath
(or filter) that has at least a portion permeable to the liquid. An
optical fiber and mirror arrangement introduces light into the chemical
sensor to interact with the analytes in the sample liquid and reflects
light through the optical fiber arrangement out of the chemical sensor.
The optical fiber and the mirror are disposed in the sheath such that one
or both can be slid along the sheath. This slidable movement can be used
to force fluid into or out of the chemical sensor through the sheath. The
sheath, which generally is impervious to particulate matters, prevents
them from entering the chemical sensor. After a certain amount of fluid
has been filtered through the sheath and collected inside the chemical
sensor, the fluid can be forced through (to back flush) the sheath to
dislodge the particulate matters that have accumulated on the outer
surface of the sheath. By doing so, the filtration (or permeability )
capability of the sheath can be restored to an acceptable degree so that
another sample fluid can be analyzed. Methods of using and making the
chemical sensor are also provided in the present invention.
Because of the ability of the chemical sensor of the present invention to
dislodge particulate matters from its outer surface, it can be
advantageously used to analyze analytes in dispersive media (i.e., liquids
with particulate matters). Furthermore, since the driving force for
dislodging the particulate matters comes from within the sensor, no
external structure is needed to direct any cleaning fluid toward the
sheath. The chemical sensor is mechanically simple and can be made
relatively small. Therefore, it can be used in a small volume of sample
liquid and in a congested space. This is particularly beneficial in
situations wherein in situ cleaning is desired, for example, in
fermentation monitoring. In such instances, because of the need to prevent
contamination and maintain isolation of the content of the fermentor, it
will be extremely difficult to remove the chemical sensors from the
fermentor for cleaning. The use of small, mechanically simple chemical
sensors and the ability to repeatedly use the same sensors without removal
from the fermentors for cleaning, as provided by the present invention,
can provide valuable information without taking too much room or risking
the introduction of foreign matters into the sample liquid. The slender
and somewhat flexible nature of optical fibers render them uniquely
appropriate for transmitting information in and out of the chemical sensor
and yet capable of maintaining fluid-tight seal with the sheath as the
optical fiber bundle slides relative to the sheath. Likewise, in an
embodiment wherein the mirror is located at an end of an optical fiber, it
can be slid relative to the sheath in a similar manner.
BRIEF DESCRIPTION OF THE DRAWING
The following figures, which show the embodiments of the present invention,
are included to better illustrate the chemical sensors of the present
invention. In these figures, wherein like numerals represent like features
in the several views, and wherein features are not dram to scale:
FIG. 1 a schematic representation of a sectional view of an embodiment of
the chemical sensor of the present invention;
FIG. 2 shows an isometric view of a portion of another embodiment of the
chemical sensor in the present invention;
FIG. 3 is a schematic representation of a sectional view of another
embodiment of the chemical sensor in the present invention; and
FIG. 4 is a schematic representation of a sectional view of yet another
embodiment of the chemical sensor in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The chemical sensor of the present invention has a feature for cleaning
particulate matters from the outer surface of a sheath of the chemical
sensor by forcing a fluid through the sheath.
FIG. 1 is a schematic representation of a preferred embodiment of the
chemical sensor of the present invention. The chemical sensor 1 has a
sheath 10 that is permeable to a fluid (or solvent) suspected of
containing a target chemical (in a dissolved form) to be analyzed. An
optical fiber bundle 12 is slidably associated with the sheath 10 so that
an interfacing portion 14 of the bundle is slidably disposed in (or
encircled or surrounded by) the sheath. In other words, the optical fiber
bundle 12 can slide on the inside surface of the sheath 10. A mirror (or
reflector) 18 is disposed inside the sheath 10 for reflecting light
emitted from the interfacing end 34 of the optical fiber bundle 12. As
used herein, the term "interfacing portion" or "interfacing end" refer to
the portion or end of the optical fiber or optical fiber bundle that is
proximate to the mirror.
The sheath can be made of any appropriate material to provide a filtration
capability (i.e., act as a filter) for the removal of particulate matters.
It may be made of, for example, fibrous or membranous materials. Materials
suitable for making filters that can remove particulate matters from
liquid samples are known in the art. Preferably, the sheath is hollow,
cylindrical, and made of a membrane that is permeable to the fluid, which
is preferably a liquid, containing the target chemical. Often, for
example, in fermentation, food processing, environmental analysis, etc.,
the fluid containing the analyte (target chemical) will be water. However,
it is contemplated that the sheath can be selected from appropriate
materials so that other liquid samples (such as organic liquids, e.g.,
ethanol, toluene) containing a target chemical can be analyzed with a
chemical sensor containing an appropriate sheath. The sheath 10 is
constructed so that it preferably is selectively permeable to a dissolved
chemical of molecular weight from about 10 Daltons to 100,000 Daltons.
Such filters (or membranes) will allow molecules and ions as small as
H.sub.3 O.sup.+ and as large as penicillin to pass through. More
preferably, to maintain a longer useable life, the sheath is made of a
material that is porous to allow passage of substances smaller than the
smallest undesirable particulate in the medium (e.g., 0.2 .mu.m in
bacterial culture media or 0.4 .mu.m in blood sample) and is impervious to
larger particulate matters. Such filters will keep out particles the size
of bacteria (about 0.2 .mu.m) and larger. In this way, when the chemical
sensor is placed in a sample fluid containing particulate matters and the
fluid is passed through the sheath 10 into a compartment (or sensor cell
or sample region) 20, the particulate matters larger than the pore size
will be retained on the outer surface 22 of the sheath 10. This kind of
chemical sensors can be used, for example, in a fermentor to monitor a
fermentation process. In many cases, a sheath that is impervious to
particulate matters of larger than about 2 .mu.m will be adequate to
remove dirt, sand, etc. Such a chemical sensor can be useful in
environmental analysis.
The optical fiber bundle 12 contains one or more optical fibers (e.g.,
fibers 23-29). In this embodiment, the interfacing portion 14 of the
optical fiber bundle 12 is slidably disposed in the sheath 10 to effect a
fluid-tight seal. The optical fiber(s) can be embedded in a suitable
material (e.g., a polymer, glass, etc.) to form a structure that conforms
to the cross-sectional shape of the sheath to prevent leakage of fluid
around the optical fiber bundle. Additionally and optionally, supporting
structures, such as a steel wire, and other mechanisms (e.g., a fiber for
conducting ultrasonic waves) can also be incorporated in the optical fiber
bundle 12. If desired, different optical fibers can be used for
transmitting light into and out of the sample region.
In the preferred embodiment of FIG. 1, the mirror 18 is firmly secured
inside the sheath so that it is fluid-tight around the mirror. In this
way, the optical fiber bundle 12, the mirror 18, and the inner surface 32
of the sheath 10 confines the sample region 20. The sample region 20 is
fluid-tight except through the sheath which is permeable to the liquid.
The mirror 18 and the optical fiber bundle 12 are so arranged in the
sheath that the mirror reflects light emitted by the interfacing end of
the optical fiber bundle 12 back to the optical fiber bundle. Light
emitted by the optical fiber bundle 12 interacts (i.e., by absorption,
fluorescence, etc.) with the target chemical. Light emitted in the light
interaction (optical interaction) can also be reflected by the mirror 18
to the optical fiber bundle 12.
Fluid can be passed into the sample region 20 by sliding the optical fiber
bundle 12 in a direction away from the mirror to create a negative
pressure in the sample region relative to the outside surface 22 of the
sheath 10. As fluid is driven through the sheath into the sample region 20
by the pressure differential across the sheath, particulate matters larger
than the pores of the sheath will be retained by the sheath, depositing on
the outer surface 22 thereof. On the other hand, the optical fiber bundle
12 can be pushed towards the mirror 18 to decrease the volume of the
sample region 20. This increases the pressure in the sample region 20 and
drives the fluid through the sheath 10 to its outer surface 22. As the
fluid traverses through the sheath 10, it dislodges the particulate
matters deposited on the outer surface 22 of the sheath, thereby cleaning
the sheath to restore at least some of the filtering capacity so that a
new sample of fluid can be driven into the sample region 20 to be
analyzed.
Preferably, when the outer surface 22 of the sheath 10 is to be cleaned,
the optical fiber bundle 12 is pushed so that it abuts the mirror 18 to
minimize residual fluid retained in the sample region 20 so that a new
sample can be dram therein for analysis with little or no dilution by the
old sample residue. Optionally, the mirror can be associated with a fiber
(e.g., optical fiber) that extends from inside the sheath 10 to the
outside in a direction opposite to that of the optical fiber bundle. This
enables the mirror to be slid in the sheath in a fluid-tight manner to
facilitate moving fluid in or out of the sample region 20 through the
sheath 10.
The sheath can be made of a material so that it is impervious to a selected
liquid but is permeable to a gaseous target chemical. The gaseous target
chemical that is dissolved or contained in the selected liquid can be
analyzed by passing the gaseous target chemical into the sample region by
pervaporation. Gases that can be analyzed in this matter include, but are
not limited to, methanol, ethanol, acetone, etc. A volume of such gaseous
material that accumulates in the sample region 20 can then be forced
through the sheath 10 to dislodge particulate matters deposited on the
outer surface 22 of the sheath. Gases and permeable membrane combinations
that permit pervaporation are known in the art.
It is preferred that the sheath is constructed such that it has the
mechanical integrity to maintain its shape when fluid is passed in and out
of the sample region 20 through the sheath 10. The dimensions of the
sheath 10 are selected, depending on, for example, the pore size,
porosity, permeability, and the amount and the size of the particulate
matters in the fluid sample. The dimensions are selected such that the
particulate matters of selected sizes can be excluded by the sheath and
the mechanical integrity of the chemical sensor can be maintained through
cycles of filtration and cleaning. Preferably, the sheath is made of a
polymer, examples of which include but are not limited to polysulfone,
polypropylene, cellulosic polymer, silicone rubber or its derivative,
polyethylene, and a composite thereof. The sheath can also be made of an
inorganic membrane such as a porous ceramic. For example, the sheath can
be about 50 .mu.m to 10 mm thick and about 5 mm to 50 mm in diameter for a
polymeric membrane of 0-80% porosity, 0.2 .mu.m (nominal) pores, for use
in an aqueous media. The distance between the mirror and the interfacing
end 34 of the optical fiber bundle is selected so that an adequate amount
of fluid can be collected in the sample region 20 for analysis and an
adequate amount of light can be emitted from the optical fiber bundle 12
and reflected by the mirror 18 such that adequate light interaction (of
excitation light with the target chemical in the sample) results to enable
analysis. For example, the distance can be about 5.0 .mu.m to 500 or more
.mu.m in the above chemical sensor.
If desired, as shown in FIG. 2, a supporting structure 36, having openings
38 can be used for supporting the sheath. The openings 38 allow fluid to
access the sheath. In FIG. 2, the supporting structure 36 is generally
cylindrical, tubular and conforms to the outer surface 22 of the sheath 10
so that when fluid is forced through the sheath to clean the outer surface
thereof by back-flushing, the supporting structure 36 prevents the
outwardly directing pressure from substantially increasing the diameter of
the sheath. Likewise, a supporting structure can be disposed on the inner
surface 32 to support the sheath when fluid is driven into the sample
region 20.
FIG. 3 shows an embodiment of a chemical sensor 19 of the present invention
wherein a sensing matrix (e.g., sensing matrix 42 on the optical fiber 46)
is disposed at the tip of at least one optical fiber of the optical fiber
bundle 12. The sensing matrix (or matrices) is selected to be sensitive to
one or more of the target chemicals (analytes) of interest. Although it is
preferable to dispose the sensing matrices at the tips of the optical
fibers, other configurations, such as on the sides of the optical fibers,
can also be used. Techniques for using sensing matrices for detecting
specific target chemicals are known in the art (e.g., U.S. Pat. No.
5,176,882, issued to Gray et. al., the dyes and methods of application
disclosed by Gray, et at. are incorporated by reference herein).
Typically, a sensing matrix has a doped polymer which immobilizes a
fluorescence dye sensitive to the target chemical of interest. Light
emitted by the optical fiber bundle 12, when interacts with (excites) the
target chemical, results in a change in either light intensity or
wavelength. This change is transmitted through the optical fiber(s) in the
optical fiber bundle 12 to a detector (not shown in the figures) such as a
spectrum analyzer.
FIG. 4 shows an embodiment of the chemical sensor of the present invention
in which more than one sensing matrices are located at the tips of optical
fibers. This chemical sensor 43 allows the detection of more than one
target chemical. For example, the sensing matrix 42 is sensitive to pH and
potassium ion while sensing matrix 44 is sensitive to oxygen.
Additionally, the optical fibers in the optical fiber bundle 12 can be
arranged such that their interfacing ends are each at a different distance
from the mirror 18. This is done to optimize the signal to noise ratio in
the detection of different target chemicals in which lights of different
wavelengths are involved. This is because the balance of the need to have
an adequate amount of the target chemical present and the need for an
adequate amount of excitation lights may be different for different target
chemicals. For example, optical fiber 46 and optical fiber 48 are disposed
in the sheath such that their corresponding sensing matrices 42 and 50 are
at different distances from the mirror 18. Also, some of the fibers (e.g.,
fiber 52) need not have any sensing matrix disposed at the tip thereof.
Such bare fibers can be used to conduct light from the sample region 20 to
perform remote spectroscopy. Such remote spectroscopy can be done by using
additional analytical equipment (not shown) at a site remote from the
chemical sensor.
By using the chemical sensor of the present invention, the presence of
target chemical(s) can be analyzed. The intensity of the light interaction
can be detected and analyzed to obtain information on the concentration of
target chemical(s). Although the illustrative embodiments of the present
invention have been described in detail, it is to be understood that the
above-described embodiments can be modified by one skilled in the art,
especially in sizes and shapes and combinations of various described
features, without departing from the spirit and scope of the invention.
For example, instead of the optical fiber bundle or the mirror, both the
optical fiber bundle and the mirror can be slid along the sheath to force
fluid through the sheath. A mechanized (e.g., motorized, pneumatic) means
can be used to drive the sliding movement. Also, an optical fiber can be
used for transmitting light both to and from the sample region.
Top